Auto calibration method and ois camera using the same

ABSTRACT

An auto calibration method and an optical image stabilizer (OIS) camera using the same are provided. The auto calibration method includes removing a DC offset of a gyroscope. A vibrator signal applied by operating a vibrator, and an actual measurement value of the gyroscope is obtained using the applied vibrator signal. A first gain value for compensating for sensitivity of the gyroscope is calculated using the vibrator signal and the actual measurement value of the gyroscope, and an actuator is operated. A displacement of a pixel actually moving on an image is moved under an operation of the actuator. A second gain value for controlling a sensitivity variation of the actuator is calculated based on the displacement of the actually moving pixel. Accordingly, it is possible to reduce processing time and to ensure high performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/360,233, filed May 22, 2014, which is the U.S. National StageApplication of International Patent Application No. PCT/KR2012/005435,filed Jul. 9, 2012, which claims priority to Korean Application No.10-2011-0125996, filed Nov. 29, 2011, the disclosures of each of whichare incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an auto calibration method and anoptical image stabilizer (OIS) camera using the same, and moreparticularly, to an auto calibration method and an OIS camera using thesame, which can overcome a variation level caused in the manufacturingstate of a gyroscope and an actuator and obtain reliable performance.

BACKGROUND ART

In an optical image stabilizer (OIS) camera, three components are addedto a typical auto focusing (AF) camera. First, the OIS camera includes agyroscope sensor for sensing tremor. The gyroscope sensor generally hasa function of sensing degrees of tilting with respect to two axes (pitchand yaw). Second, the OIS camera includes an actuator for compensatingfor tilting of the camera when tremor occurs. Third, the OIS cameraincludes an OIS control large scale integration (LSI) chip forcontrolling the gyroscope sensor and the actuator.

Among the three components, the gyroscope sensor and the actuator cannotachieve normal performance when the OIS control LSI chip does notcorrect a variation between products in a manufacturing state.Typically, the OIS control LSI chip necessarily includes a gainamplifying circuit to control the ratio of output to input, and a modulemanufacturer performs an individual calibration method for eachcomponent through the control of the gain amplifying circuit.

To this end, the typical method includes two methods. First, there is amethod of manually searching for a gain value so as to provide the samevalue to all modules. In this case, the processing time can bedecreased, but it is difficult to ensure exact OIS performance when thedistribution between components is large. Second, there is a method ofautomatically searching for a gain value through an image test. In themethod, although the distribution between components is large, it can beexpected to ensure exact OIS performance to some degree. However, theprocessing time is considerably increased according to gain controlresolution, the evaluation method is complicated, and the processingcost is increased.

Therefore, it is difficult to decrease the processing time and to ensurethe exact OIS performance using the typical method, and hence it isrequired to provide a plan capable of solving such problems.

DISCLOSURE Technical Problem

The present invention is conceived to solve the aforementioned problems.Accordingly, an object of the present invention is to provide an autocalibration method and an optical image stabilizer (OIS) camera usingthe same, which can decrease processing time and ensure highperformance.

Technical Solution

According to an aspect of the present invention, there is provided anauto calibration method having a gyroscope for sensing tremor and anactuator for compensating for tilting of a camera when the tremoroccurs, the method including: removing a DC offset of the gyroscope;applying a vibrator signal by operating a vibrator, and obtaining anactual measurement value of the gyroscope using the applied vibratorsignal; calculating a first gain value for compensating for sensitivityof the gyroscope using the vibrator signal and the actual measurementvalue of the gyroscope; operating the actuator; measuring a displacementof a pixel actually moving on an image under an operation of theactuator; and calculating a second gain value for controlling asensitivity variation of the actuator based on the displacement of theactually moving pixel.

The auto calibration method may further include storing the first andsecond gain values.

The vibrator signal may be a triangular wave signal, and the calculatingof the first gain value may include determining, as the first gainvalue, a value obtained by dividing the scope of the triangular wavesignal by the actual measurement value of the gyroscope.

The calculating of the first gain value may include determining, as thefirst gain value, a value obtained by dividing an average of angularvelocity by the actual measurement value of the gyroscope when thevibrator signal does not have the same slope.

The vibrator signal may be a sine wave signal, and the calculating ofthe first gain value may include determining, as the first gain value, avalue obtained by dividing a calculated angular velocity of the sinewave signal by the actual measurement value of the gyroscope.

The calculating of the second gain value may include determining, as thesecond gain value, a value obtained by dividing a reference coordinatedisplacement by the displacement of the actually moving pixel.

The auto calibration method may further include storing a signalcalibrated by removing the DC offset.

The removing of the DC offset may be performed in a state in which thevibrator is stopped.

The first gain value may be a gain value of an amplifying circuit forcompensating for a variation level of sensitivity tolerance of a currentgyroscope.

According to another aspect of the present invention, there is providedan optical image stabilizer (OIS) camera, including: a gyroscopeconfigured to sense tremor; an actuator configured to compensate fortilting of the camera when the tremor is sensed by the gyroscope; and acontroller configured to perform gain calibration of the camera bycalculating a first gain value for compensating for sensitivity of thegyroscope and a second gain value for controlling a sensitivityvariation of the actuator.

The controller may obtain an actual measurement value of the gyroscopeby generating a signal from a vibrator, and calculate the first gainvalue for compensating for the sensitivity of the gyroscope using theactual measurement value.

The signal generated from the vibrator may be a triangular wave signal,and the controller may determine, as the first gain value, a valueobtained by dividing the scope of the triangular wave signal by theactual measurement value of the gyroscope.

The signal generated from the vibrator may be a sine wave signal, andthe controller may determine, as the first gain value, a value obtainedby dividing a calculated angular velocity of the sine wave signal by theactual measurement value of the gyroscope.

The controller may measure a displacement of a pixel actually moving onan image under an operation of the actuator, and calculate the secondgain value based on the displacement of the actually moving pixel.

The OIS camera may further include a storage configured to store asignal calibrated by removing the DC offset when the DC offset of thegyroscope is removed.

Advantageous Effects

According to the auto calibration method and an optical image stabilizer(OIS) camera using the same configured as described above, it ispossible to decrease processing time and cost and to ensure highperformance.

DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart illustrating an auto calibration method in anoptical image stabilizer (OIS) camera according to an embodiment of thepresent invention.

FIG. 2 is a view illustrating a process of removing a DC offset using agyroscope, in the auto calibration method in the OIS camera according tothe embodiment of the present invention.

FIG. 3 is a view illustrating a process of obtaining a signal using thegyroscope, in the auto calibration method in the OIS camera according tothe embodiment of the present invention.

FIG. 4 is a view illustrating a process of measuring a coordinatedisplacement of a pixel, in the auto calibration method in the OIScamera according to the embodiment of the present invention.

FIG. 5 is a block diagram illustrating an operation of an OIS camera towhich the auto calibration method is applied according to an embodimentof the present invention.

BEST MODE FOR INVENTION

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which embodiments of the presentinvention are shown. This present invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure is thorough, and will fully convey the scope of thepresent invention to those skilled in the art.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another element. Thus, a “first” element discussedbelow could also be termed as a “second” element without departing fromthe teachings of the present invention.

It will be understood that when an element is referred to as being“coupled” or “connected” to another element, it can be directly coupledor connected to the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlycoupled” or “directly connected” to another element, there are nointervening elements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be further understood that the terms “includes” and/or“including,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence and/or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof.

In the drawings, the thickness of layers, films and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout.

FIG. 1 is a flowchart illustrating an auto calibration method in anoptical image stabilizer (OIS) camera according to an embodiment of thepresent invention.

First, the auto calibration method starts in a still state of the camera(S100). That is, a vibrator is necessarily in the still state. In afirst step, calibration is performed to a level of zero by removing anoffset (S110).

Step S110 is shown in FIG. 2. FIG. 2(a) shows a signal (sine wave)obtained by a gyroscope when a sine wave is vibrated, and FIG. 2(b)shows a signal in which an offset occurs according to a manufacturingstate. That is, when assuming that the signal is a sine wave signal, thesignal has an offset of C₀ according to the manufacturing state. If thesignal in this state passes through an integrator of an OIS controller,the value of a gyro signal is accumulated as an error value inproportion to time. Thus, the first step includes a process of removingthe offset. The error value may be stored in a storage module, e.g., anelectrically erasable programmable read-only memory (EEPROM).

Next, the gyro signal is obtained (S120).

Step S120 is shown in FIG. 3. First, the vibrator is operated to detectan actual measurement value of the gyro signal. It is sufficient thatthe vibrator detect only the maximum of angles that can be adjusted byan actuator. Thus, a triangular wave having the same slope is inputted.However, when there is a problem in implementing the triangular wave, ageneral sine wave signal may also be inputted. Here, the differentialvalue of the same slope is received as an angular velocity (unit: dps(degree per second)) in the gyroscope.

FIG. 3(a) shows a vibrator signal. That is, the vibrator signal havingthe same slope is applied. FIG. 3(b) shows an angular velocity obtainedthrough the gyroscope based on the input vibrator signal. Since thetriangular wave signal having the same slope has been applied, theangular velocity value “a” received by the gyroscope is constant. Thus,the camera including the gyroscope has a characteristic of the actualmeasurement value “a.” If the vibrator does not obtain a signal havingthe same slope due to a reproduction problem, the average of angularvelocity values obtained in a certain time T may be applied to theactual measurement value.

Next, a first gain value is calculated. The first gain value is a valueused to determine a gain (dB) level of an amplifying circuit forcompensating for a variation level with respect to sensitive toleranceof the gyroscope. The first gain value may be calculated by thefollowing Equation 1.

$\begin{matrix}{{{First}\mspace{14mu} {gain}\mspace{14mu} {value}} = \frac{{Slope}\mspace{14mu} {of}\mspace{14mu} {triangular}\mspace{14mu} {wave}}{{Actual}\mspace{14mu} {measurement}\mspace{14mu} {value}\mspace{14mu} {of}\mspace{14mu} {gyroscope}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In Equation 1, the numerator denotes a slope of a triangular wave of thevibrator, which is a reference value. The denominator denotes an actualmeasurement value in the vibrator, obtained through the processdescribed above. The first gain value is determined by dividing thereference value of the slope by the actual measurement value of theslope.

When assuming that the signal of the vibrator is a sine wave, thereference value of the numerator is not the slope of the triangular wavebut is the maximum triangular velocity of the vibrator. The angularvelocity of the vibrator is generally expressed by the followingEquation 2 using a vibrator angle and a vibrator frequency.

Maximum angular velocity of sine wave=2π×vibrator frequency×vibratorangle  Equation 2

If the vibrator has a sine wave of ±0.5/5 hz based on the vibrator angleof zero, the maximum angular velocity (dps) of the sine wavecorresponding to the numerator becomes 2*π*5 hz*1 degrees. In this case,the actual measurement value of the gyroscope is also an angularvelocity (dps), and thus the first gain value is determined as maximumangular velocity of sine wave/actual measurement value of gyroscope.

The first gain value is stored in the storage module, e.g., EEPROM, etc.(S180). The first gain value is used to compensate for the gyrosensitivity of a current module.

The next step illustrates a process of calculating a second gain value.

First, an actuator is operated (S150). The current value for operatingthe actuator is identical to that determined by the reference value instep S170 which will be described later.

If the actuator is operated, the coordinate displacement of a pixel ismeasured (S160). Step S160 is shown in FIG. 4. That is, the Y-axis andX-axis displacements of the pixel actually moving on an image aremeasured by the operation of the actuator. In this case, thedisplacement of the pixel is a displacement including the tolerance ofan effective focal length (EFL) of the current module.

The reason why the displacement of the actuator is considered as thedisplacement of the pixel is that correction is performed including evena variation that may be generated by the tolerance of the EFL of thecamera. Since the pitch of a sensor pixel is constant, the displacementof an actual stroke is not applied to the displacement of the pixel.

The displacement of the pixel may be calculated by the followingEquation 3.

$\begin{matrix}{{{Displacement}\mspace{14mu} {of}\mspace{14mu} {pixel}} = \frac{{Stroke}\mspace{14mu} {of}\mspace{14mu} {actuator}}{{Pixel}\mspace{14mu} {pitch}\mspace{14mu} {of}\mspace{14mu} {image}\mspace{14mu} {sensor}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Here, the stroke of the actuator denotes a value obtained by multiplyingEFL (effective focal length) and TAN (correction angle).

The second gain value is calculated based on the displacement of thepixel, calculated as described above (S170). The displacement of thepixel is calculated by respectively measuring displacements of x and ycoordinates. The displacements are used as actually measureddisplacements by the following Equation 4.

$\begin{matrix}{{{Second}\mspace{14mu} {gain}\mspace{14mu} {value}} = \frac{{Reference}\mspace{14mu} {coordinate}\mspace{14mu} {displacement}}{{Acutally}\mspace{14mu} {measured}\mspace{14mu} {displacement}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Here, the reference coordinate displacement is an arbitrary value. Anarbitrary current value is determined as many as a correctable angle, inconsideration of the level of current application to actual stroke,possessed by the actuator.

Finally, the calculated second gain value is stored in the storagemodule (S180). That is, the second gain value is stored in storage suchas EEPROM to use the calibration of sensitivity variation.

The auto calibration method in the OIS camera according to theembodiment of the present invention is divided into two processes, i.e.,a gyro sensitivity calibration process and an actuator sensitivitycalibration process. The auto calibration method is identicallyperformed on both the pitch and yaw axes. Accordingly, the variationlevel caused in the manufacturing states of the gyroscope and theactuator is overcome, so that it is possible to ensure the performanceof the camera as much as possible, to exactly apply the variation levelto the camera and to perform the processes at low cost for a shortperiod of time.

FIG. 5 is a block diagram illustrating an operation of an OIS camera towhich the auto calibration method is applied according to an embodimentof the present invention.

As shown in FIG. 5, the OIS camera according to the embodiment of thepresent invention includes a gyroscope 200, an actuator 230, acontroller 210 and a storage 240.

First and second gain values 202 and 220 are obtained as described inthe aforementioned method. Therefore, the detailed description of themethod will be omitted. The first gain value 202 passes through thecontroller 210 so that the second gain value 220 is derived, and thesecond gain value 220 is used to calibrate sensitivity of the actuator230. Specifically, the first gain value 202 passes through a first highpass filter 212, an integrator 214, a second high pass filter 216 and aphase filter 218 in the controller 210.

Meanwhile, the first and second gain values 202 and 220 may be stored inthe storage 240. In the conventional method, only the second gain valueis calibrated using a calibration method through image processing ormanual calibration method. That is, the second gain value is correctedafter a gyro signal passes through the integrator and changes into anangle and before determining a value to be transferred to the actuator.However, in the OIS camera according to the embodiment of the presentinvention, the sensitivity compensation of the gyroscope isdistinguished from that of the actuator, so that two types of valuessuch as the first and second gain values 202 and 220 are stored in thestorage 240.

Accordingly, it is possible to remarkably reduce processing time and toperform correction by exactly applying individual vibrations, and thusthe performance of the OIS camera can be ensure. Further, the automationis possible using the method of the present invention, so that massproduction is possible, thereby reducing production cost.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the present invention is notlimited to the embodiments but rather that various changes ormodifications thereof are possible without departing from the spirit ofthe present invention. Accordingly, the scope of the present inventionshall be determined only by the appended claims and their equivalents.

What is claimed is:
 1. An auto calibration method having an actuator forcompensating for tilting of a camera when the tremor occurs, the methodcomprising: operating the actuator; measuring a displacement of a pixelactually moving on an image under an operation of the actuator; andcalculating a first gain value for controlling a sensitivity variationof the actuator based on the displacement of the actually moving pixel.2. The method of claim 1, further comprising storing the first gainvalues.
 3. The method of claim 1, wherein the calculating of the firstgain value includes determining the first gain value by dividing areference coordinate displacement by the displacement of the actuallymoving pixel.
 4. The method of claim 1, wherein the first gain value isa gain value of an amplifying circuit for compensating for a variationlevel of sensitivity tolerance of a gyroscope.
 5. An optical imagestabilizer (OIS) camera, comprising: a gyroscope configured to sensetremor; an actuator configured to compensate for tilting of the camerawhen the tremor is sensed by the gyroscope; and a controller configuredto perform gain calibration of the camera by calculating a first gainvalue for compensating for sensitivity of the gyroscope and a secondgain value for controlling a sensitivity variation of the actuator. 6.The OIS camera of claim 5, wherein the controller obtains an actualmeasurement value of the gyroscope by generating a signal from avibrator, and calculates the first gain value for compensating for thesensitivity of the gyroscope using the actual measurement value.
 7. TheOIS camera of claim 5, wherein the controller is configured to measure adisplacement of a pixel actually moving on an image under an operationof the actuator, and calculate the second gain value based on thedisplacement of the actually moving pixel.
 8. The OIS camera of claim 5,further comprising a storage configured to store a signal calibrated byremoving the DC offset when the DC offset of the gyroscope is removed.